When summer hits, the combination of heat and activity often result in increased sweating. Sweat is great - it's our personal evaporative cooling system. Most of us will sweat out at least half a litre each day , and that's before any intense exercise.
Author
- Daniel Eldridge
Senior Lecturer in Chemistry, Swinburne University of Technology
Unfortunately, sweating can also exacerbate body odour. To control this, many of us use an antiperspirant or deodorant every day. Even though we apply both to our underarms, the two products are actually distinct and function in different ways.
Knowing this difference can help you troubleshoot your personal hygiene products - and stay stink free.
Sweat doesn't smell
To understand how underarm products work, we first need to look at where the unpleasant odour comes from.
The sweat our bodies release is actually odourless . It comes primarily from one of two types of glands: eccrine and apocrine.
Eccrine sweat glands, responsible for the greatest amount of sweat, are located over most of the body. They tend to release a mostly water-based sweat primarily responsible for our thermoregulation . This sweat also contains electrolytes and small amounts of other substances that typically don't result in bad odours.
The apocrine sweat glands, found primarily in the armpit and groin regions, produce sweat with a more oily composition , containing proteins, sugars and oils. This sweat is also odourless at first.
However, several types of bacteria that live on the skin feed on this sweat, and in doing so, produce volatile and odorous substances . They cause body odour, and the scent of some of these compounds can be sensed by nose in concentrations of trillionths of a gram per litre of air . Apocrine sweat glands tend to become active at the onset of puberty.
To combat these odours, we reach for antiperspirants or deodorants. Although we tend to use the terms interchangeably, each name actually describes the precise way these products work.
What antiperspirants do
Broadly speaking, all antiperspirants work in the same way. They contain active ingredients that stop your body from releasing the sweat in the first place.
The ingredients that do this are usually one of a variety of metal-containing salts, most frequently aluminium chlorohydrate, aluminium sesquichlorohydrate, aluminium chloride, or a zirconium-aluminium compound.
These combine with water and other molecules in the sweat gland to produce a temporary plug that prevents the flow of sweat to the skin's surface. As a result, the bacteria on your skin are deprived of the substances they digest to produce unwanted odours.
What deodorants do
Deodorants work differently - they allow sweat to flow out onto the skin, but then prevent the odour either from being released, or from becoming detectable. This is achieved with a range of different ingredients .
Some deodorants may have antimicrobial agents , designed to reduce the microbial population responsible for producing the odorous molecules. Some are perfumes , designed to mask unwanted odours.
Other compounds are sometimes added as odour absorbers to bind volatile molecules, and sometimes to absorb moisture too.
Finally, selected active ingredients may alter the local pH level of your skin, making it less hospitable for bacteria.
Other approaches - currently in development - look to inhibit bacteria from producing odours, or to neutralise odour precursors before the bacteria can consume them.
There's some overlap, too
Outside of these main ingredients, you can expect your underarm product to contain a few other additives - to work as preservatives, provide a pleasant fragrance, assist with application, and improve the feel of the product on your skin.
If you're just looking to stop the smell, a deodorant can get the job done. If you want to sweat less too, an antiperspirant is what you need. If you can't decide, quite a few products use a combination of both strategies - a strongly scented antiperspirant, or antiperspirants with antimicrobials are common examples.
As with many consumer products, some people will have either personal or outcome-based preferences for one approach over another. As we age and change habits , our bodies may respond differently to these products, so you may need to engage in some trial and error, or even to seek medical advice in some cases.
What about 'natural' deodorants?
Despite a rumour started by an email hoax , evidence-based research indicates aluminium-based antiperspirants are safe, and don't pose any risks to our health .
That said, "natural" deodorants are popular for various reasons. Although they sometimes use different active ingredients compared to "regular" deodorants, the mode of action is usually the same - antibacterial, masking the smell, absorbing moisture or a combination thereof.
One common active ingredient in "natural" formulations is sodium bicarbonate, used to absorb moisture and odour, and to modify the underarm pH. Certain essential oils, used for their antimicrobial properties and scent, are common ingredients too.
Importantly, a product being "natural" does not necessarily mean that it's safer . In fact, some alternative deodorant ingredients haven't been as thoroughly tested for safety. Others pose the same risks as their synthetic counterparts - for example, that bacteria might develop antimicrobial resistance against both synthetic ingredients and natural ones, such as essential oils.
Daniel Eldridge does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
